This invention relates to a projector for projecting light to indicate a measurement area and a measuring device provided with such a projector for remotely measuring a surface temperature of an object to be measured.
In a known projector for use in a radiation thermometer for remotely measuring a surface temperature of a measurement object, a laser beam source is disposed on an optical axis branched from a main optical axis of a measurement optical system for converging a radiant energy from a measurement object, and a point of measurement is indicated by forming a spot projection image on the measurement object by the laser beam source.
However, this projector is merely capable of indicating the center of the measurement area, but is incapable of constantly forming a projection image for a variety of measurement objects. Further, since this device does not indicate the outline of the measurement area, it is difficult to accurately visually confirm the measurement area.
U.S. Patent No. 5,368,392 discloses a projector for use in a radiation thermometer which is so constructed as to form a ring-shaped projection image indicative of the outline of a measurement area on a measurement object. In this projector, to form the ring-shaped projection image, there is provided a mechanism for mechanically rotating a reflector for reflecting a laser beam. More specifically, in this mechanism, the reflector is inclined with respect to a line parallel with an optical axis of the radiation thermometer. The laser beam is directed at a predetermined angle with respect to the optical axis of the radiation thermometer. The reflector is rotated to reflect the inclined laser beam to produce a ring-shaped projection image on the measurement object. However, the laser beam is reflected with respect to an optical axis different from the optical axis along which the laser beam is emitted. This makes it difficult to accurately produce a ring-shaped projection image.
Also, this U.S. patent discloses a mechanism for mechanically rotating the laser beam source about an optical axis. However, the direct rotation of laser beam source makes the construction of the projector complicated.
Also, this projector is merely capable of indicating the outline of the measurement area by the ring-shaped projection image, but incapable of indicating the center of the measurement area. Accordingly, the use of this projector is not suitable in the case that the fine adjustment of the optical axis is required.